I just received this radio from Ebay untested. When powered up there is no audio. It transmits fine. Nothing on PA either. Any ideas what the problem could be???? Thanks Dan
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- Thread starter danmcclain
- Start date
I'd like to know too...
The thing uses a mod transformer, so to me it indicates work on Talkback issues, you have AM so that tells me one live side of the transformer works - no PA relates to the output winds of the mod transformer that connects to the other open lead pair side.
So check CB/PA switch - look for problems in and around the EXT SP and PA jacks.
Also check squelch function - if you don't hear a "thunk" from the radios speaker during power up (the bootstrap) it might mean the Audio TA7222P chip needs help - new caps are probably what it is calling for. Affects SQ function too.
ADDED IN:
The radio uses a RELAY from Pin 4 to offer switching for the SPEAKER ground.
Might want to check that...
Also - since you may not have Receive, but shows RX and TX switching - Pin 1 and Pin 2 of the MIC JACK may have been reversed.
Check Board ground to Pin 2 of the Jack, if it shows a Dead short, there is your problem.
Then what about Pin1? That is should be your Audio (Mic line)
Here's why...
Service manual shows EPT012910A but wired for typical Cobra Uniden 4-pin Handset style.
Pin 1 - GND
Pin 2 - MIC
Pin 3 - TX
Pin 4 - RX
But look at the plug side schematically shows...
Pin 1 - MIC
Pin 2 - GND
Pin 3 - TX
Pin 4 - RX
See the swap?
So, if no noise, reverse Pin 1 and 2 - Pin 2 might need to be Ground at the HANSET to match the wiring shown on schematic. to the RADIO Jack
Short Pin 2 to Pin 4 - get RX? Theres' your answer.
Now, I'm back to Dinner with the wife...
The thing uses a mod transformer, so to me it indicates work on Talkback issues, you have AM so that tells me one live side of the transformer works - no PA relates to the output winds of the mod transformer that connects to the other open lead pair side.
So check CB/PA switch - look for problems in and around the EXT SP and PA jacks.
Also check squelch function - if you don't hear a "thunk" from the radios speaker during power up (the bootstrap) it might mean the Audio TA7222P chip needs help - new caps are probably what it is calling for. Affects SQ function too.
ADDED IN:
The radio uses a RELAY from Pin 4 to offer switching for the SPEAKER ground.
Might want to check that...
Also - since you may not have Receive, but shows RX and TX switching - Pin 1 and Pin 2 of the MIC JACK may have been reversed.
Check Board ground to Pin 2 of the Jack, if it shows a Dead short, there is your problem.
Then what about Pin1? That is should be your Audio (Mic line)
Here's why...
Service manual shows EPT012910A but wired for typical Cobra Uniden 4-pin Handset style.
Pin 1 - GND
Pin 2 - MIC
Pin 3 - TX
Pin 4 - RX
But look at the plug side schematically shows...
Pin 1 - MIC
Pin 2 - GND
Pin 3 - TX
Pin 4 - RX
See the swap?
So, if no noise, reverse Pin 1 and 2 - Pin 2 might need to be Ground at the HANSET to match the wiring shown on schematic. to the RADIO Jack
Short Pin 2 to Pin 4 - get RX? Theres' your answer.
Now, I'm back to Dinner with the wife...
Last edited:
Thanks for the info Handy Andy, was wondering why it came with a Cobra handheld mic.... Dan